Find a number which equals to the index

Given an array of positive and negative numbers sorted in ascending order.Find a number which is equal to the index of that number in array.
ex: Array = {-3,-1,0,1,4}
ans: a[4]=4
We can do it by linear search in O(n) time or by doing binary search in O(logN) time.

public class FixedPoint {
 public static void main(String[] args) {
  int[] a = { -10, -5, 0, 3, 7 };
  int fixedPoint = getFixedPointNumber(a, 0, a.length - 1);

  if (fixedPoint != -1) {
   System.out.println("Number is : " + fixedPoint);
  } else {
   System.out.println("There is Number satisying the condition.");
  }
 }

 /**
  * Returns a number a[i] which satisfies the condition a[i]=i
  * 
  * @param a
  * @param low
  * @param high
  * @return
  */
 private static int getFixedPointNumber(int[] a, int low, int high) {

  if (a == null || a.length == 0 || low < 0 || high >= a.length
    || low > high)
   return -1;

  int mid = (low + high) / 2;

  if (a[mid] == mid) {
   return mid;
  } else if (a[mid] < mid) {
   return getFixedPointNumber(a, mid + 1, high);
  } else {
   return getFixedPointNumber(a, low, mid - 1);
  }
 }

}